Under this protocol, 85-CC145 we have studied 21 patients with metastatic colon or appendiceal adenocarcinoma. All patients received I-131 B72.3 intraperitoneal (IP) (mean 8.7 mCi, .9 mg) and in addition to determine the specificity of targeting selected patients were coinfused with IP I-125 B1-3(non-specific) antibody (mean .7mCi, .9mg)/; Four additional patients received the I-131 B72.3 IP and I-125 intravenously to determine the best route of targeting peritoneal carcinomatosis. Tumor uptake was seen in 12 of 21 patients injected by the IP route. In 4 patients the antibody scan was the only evidence of metastatic disease. The 2 patients with negative scans had tumor detected only at laparotomy. Fifty percent clearance from the IP cavity occurred within 24 to 96 hours. Gamma counting of tumor specimens showed specificity of uptake and also demonstrated preferential delivery of the antibody when administered via the IP route in patients with peritoneal carcinomatosis.